Conventional containers having hermetically sealing performance based upon heat sealing include a container with flange obtained by draw-molding a laminated material which consists of laminating a thermoplastic resin film on both surfaces of a metal foil or draw-molding a laminated material consisting of a lamination of a gas-barrier resin film and a thermoplastic resin, a cup with heat-sealable closure consisting of a flexible substrate obtained by laminating a thermoplastic resin film on both surfaces of a metal foil, and a retort pouch using a laminated material obtained by laminating a thermoplastic resin film on both surfaces of a metal foil or using a laminated material obtained by laminating a thermoplastic resin film on a gas-barrier resin film, and have been used for containing foods. After the contents are packed therein and sealed, the containers are usually heated for sterilization.
Despite the foods are packed in the containers and are hermetically sealed by heating followed by sterilization by heating, however, there remains a problem in that the foods are discolored or are oxidized to lose flavor due to oxygen in the air entrapped when the foods are packed, due to oxygen contained in the foods or due to active enzymes in the foods during the storage and, especially, as they are stored for extended periods of time no matter how excellent barrier properties the containers and closures exhibit.